How do i adjust the brake pads on a hydraulic disc brakes for mountain bike?

[Dexter49]

I have been having problems with the front wheel of my bike in that it doesn't freewheel any more and after checking this weekend i found that i could see and hear right hydraulic brake pad rubbing on the disc.

I have Shimano BR - M486 brakes - i was wondering if how i could adjust this right hand pad by a millimeter or two?
What is the recommended amount? Thank You

 

[dabac]

In short - you don't. What you can do though is adjust the position of the whole caliper.
The stock recommendation is to loosen bolts, pull on brake, and tighten bolst while brake action centers the caliper.
I've found this to be more than a little hit-and-miss. Often the caliper gets nudged about a bit when tightening the bolts. I do the bolts up quarter- tight, then eyeball the gap, adjust position before clamping down harder.

Bicycle hydraulic disc brakes are supposed to work like car or motorcycle hydraulic discs. They're all low-clearance mechanisms. There's a gasket between piston and cylinder, and when the brake is activated this gasket doesn't slide as much as deform when the piston is pressed against the pad, and the pad against the rotor. Then when you ease off the brake the gasket springs back into its original shape, pulling the piston with it a millimeter or two back into the caliper. As pads wear, the gasket will slide a little outwards to compensate.